High loft spunbonded web

ABSTRACT

Herein are disclosed high loft spunbonded webs that are substantially free of crimped fibers and gap-formed fibers. The webs exhibit a solidity of from less than 8.0% to about 4.0% and a ratio of Effective Fiber Diameter to Actual Fiber Diameter of at least 1.40. Also disclosed are methods of making such webs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/497,102, filed Jul. 2, 2009, now issued as U.S. Pat. No. 8,162,153,the disclosure of which is incorporated by reference in its entiretyherein.

BACKGROUND

Spunbonded webs have found use in various applications, includingbackings for diapers and/or personal care articles, carpet backings,geotextiles and the like. Such spunbonded webs are typically low-loftmaterials which are relied upon primarily to supply structuralreinforcement, barrier properties, and so on. Some workers in the fieldhave attempted to develop webs with higher loft, by a variety ofmethods.

SUMMARY

Herein are disclosed high loft spunbonded webs that are substantiallyfree of crimped fibers and gap-formed fibers. The webs exhibit asolidity of from less than 8.0% to about 4.0% and a ratio of EffectiveFiber Diameter to Actual Fiber Diameter of at least 1.40. Also disclosedare methods of making such webs.

Thus in one aspect, herein is disclosed a spunbonded web comprising asolidity of from less than 8.0% to about 4.0% and comprising a ratio ofEffective Fiber Diameter to Actual Fiber Diameter of at least 1.40,wherein the web is substantially free of crimped fibers, gap-formedfibers, and bicomponent fibers.

Thus in another aspect, herein is disclosed a self-supporting pleatedfilter comprising filter media comprising a plurality ofoppositely-facing pleats and further comprising a perimeter framepresent along the edges of the filter media, wherein the filter mediacomprises a spunbonded web comprising a solidity of from less than 8.0%to about 4.0% and comprising a ratio of Effective Fiber Diameter toActual Fiber Diameter of at least 1.40, wherein the web is substantiallyfree of crimped fibers, gap-formed fibers, and bicomponent fibers.

These and other aspects of the invention will be apparent from thedetailed description below. In no event, however, should the abovesummaries be construed as limitations on the claimed subject matter,which subject matter is defined solely by the attached claims, as may beamended during prosecution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an apparatus which may be used to forma spunbonded nonwoven web as disclosed herein.

FIG. 2 is a side view of an attenuator which may be used in the processof FIG. 1.

FIG. 3 is a scanning electron micrograph at 100 times magnification intop view, of a conventional spunbonded nonwoven web.

FIG. 4 is a scanning electron micrograph at 250 times magnification intop view, of a spunbonded nonwoven web produced as disclosed herein.

FIG. 5 is a scanning electron micrograph at 100 times magnification incross sectional view, of a spunbonded nonwoven web produced as disclosedherein.

FIG. 6 is a perspective view, partially in section, of a pleated filterwith a perimeter frame and a scrim.

Like reference symbols in the various figures indicate like elements.Unless otherwise indicated, all figures and drawings in this documentare not to scale and are chosen for the purpose of illustratingdifferent embodiments of the invention. In particular the dimensions ofthe various components are depicted in illustrative terms only, and norelationship between the dimensions of the various components should beinferred from the drawings, unless so indicated. Although terms such as“top”, bottom”, “upper”, lower”, “under”, “over”, “front”, “back”,“outward”, “inward”, “up” and “down”, and “first” and “second” may beused in this disclosure, it should be understood that those terms areused in their relative sense only unless otherwise noted.

DETAILED DESCRIPTION

Glossary

Herein, the term “filaments” is used in general to designate moltenstreams of thermoplastic material that are extruded from a set oforifices, and the term “fibers” is used in general to designatesolidified filaments and webs comprised thereof. These designations areused for convenience of description only. In processes as describedherein, there may be no firm dividing line between partially solidifiedfilaments, and fibers which still comprise a slightly tacky and/orsemi-molten surface.

The term “meltspun” refers to fibers that are formed by extrudingfilaments out of a set of orifices and allowing the filaments to cooland solidify to form fibers, with the filaments passing through an airspace (which may contain streams of moving air) to assist in cooling thefilaments and passing through an attenuation (i.e., drawing) unit to atleast partially draw the filaments. Meltspinning can be distinguishedfrom meltblowing in that meltblowing involves the extrusion of filamentsinto converging high velocity air streams introduced by way ofair-blowing orifices located in close proximity to the extrusionorifices.

By “spunbonded” is meant a web comprising a set of meltspun fibers thatare collected as a fibrous web and optionally subjected to one or morebonding operations.

By “directly collected fibers” is meant fibers formed and collected as aweb in essentially one operation, by extruding molten filaments from aset of orifices and collecting the at least partially solidifiedfilaments as fibers on a collector surface without the filaments orfibers contacting a deflector or the like between the orifices and thecollector surface.

By “pleated” is meant a web at least portions of which have been foldedto form a configuration comprising rows of generally parallel,oppositely oriented folds. As such, the pleating of a web as a whole isdistinguished from the crimping of individual fibers.

By “crimped fibers” is meant fibers that have undergone a crimpingprocess. Crimping processes include mechanical crimping (e.g., of staplefibers). Crimping processes also include so-called thermal activationprocesses in which bicomponent fibers (e.g., so-called conjugate fibers)are exposed to temperatures such that crimping occurs due to a disparityin the shrinkage among the components of the fiber. Crimping processesalso include thermal activation processes in which geometricallyasymmetric thermal treatment of fibers is performed so as to generate asolidification gradient in the fibers thus resulting in crimping. Suchthermal activation processes or other crimping processes may occurbefore, during, or after the spunbonding process. Crimped fibers may beidentified as displaying repeating features (as manifested e.g. in awavy, jagged, sinusoidal, etc. appearance of the fiber), by having ahelical appearance (e.g., particularly in the case of crimped fibersobtained by thermal activation of bicomponent fibers), and the like, andare readily recognizable by those of ordinary skill in the art.Exemplary crimped fibers are described in U.S. Pat. No. 4,118,531 toHauser and U.S. Pat. No. 5,597,645 to Pike et al., and CA Patent 2612854to Sommer et al.

By “gap-formed fibers” is meant fibers collected in a gap (e.g., aconverging gap) between two spaced-apart surfaces (e.g., in a nip, slot,etc.). Gap-formed fibers may be identified as displaying, when a web isviewed in cross section, a generally repeating pattern of U-shaped orC-shaped fibers, and/or a generally repeating pattern of waves, folds,loops, ridges, or the like, and as having a significant number of fibersof the web being oriented generally along the shortest dimension (thethickness direction) of the web. In this context, gap-formed fibersincludes fibers as may be preliminarily collected on a single (e.g.generally flat collecting surface), and then passed through a converginggap, nip, etc., that achieves the aforementioned pattern of waves,folds, or the like. Exemplary gap-formed fibers are described in U.S.Pat. No. 6,588,080 to Neely et al., U.S. Pat. No. 6,867,156 to White etal., and U.S. Pat. No. 7,476,632 to Olson et al.

By solidity is meant a dimensionless fraction (usually reported inpercent) that represents the proportion of the total volume of a fibrousweb that is occupied by the solid (e.g. polymeric fibrous) material.Further explanation, and methods for obtaining solidity, are found inthe Examples section. Loft is 100% minus solidity and represents theproportion of the total volume of the web that is unoccupied by solidmaterial.

FIG. 1 shows an exemplary apparatus which may be used to form high loftspunbonded webs as disclosed herein. In an exemplary method of usingsuch an apparatus, polymeric fiber-forming material is introduced intohopper 11, melted in an extruder 12, and pumped into extrusion head 10via pump 13. Solid polymeric material in pellet or other particulateform is most commonly used and melted to a liquid, pumpable state.

Extrusion head 10 may be a conventional spinnerette or spin pack,generally including multiple orifices arranged in a regular pattern,e.g., straightline rows. Filaments 15 of fiber-forming liquid areextruded from the extrusion head and may be conveyed through air-filledspace 17 to attenuator 16. The distance the extruded filaments 15 travelthrough air space 17 before reaching the attenuator 16 can vary, as canthe conditions to which they are exposed. Quenching streams of air 18may be directed toward extruded filaments 15 to reduce the temperatureof, and/or to partially solidify, the extruded filaments 15. (Althoughthe term “air” is used for convenience herein, it is understood thatother gases and/or gas mixtures may be used in the quenching and drawingprocesses disclosed herein). One or more streams of air may be used;e.g., a first air stream 18 a blown transversely to the filament stream,which may serve primarily to remove undesired gaseous materials or fumesreleased during extrusion, and a second quenching air stream(s) 18 bthat may serve primarily to achieve temperature reduction. The flow rateof the quenching airstream(s) may be manipulated to advantage asdisclosed herein, to assist in achieving webs with the unique propertiesdisclosed herein.

Filaments 15 may pass through attenuator 16 (discussed in more detailbelow) and then be deposited onto a generally flat (by which is meantcomprising a radius of curvature of greater than six inches) collectorsurface 19 where they are collected as a mass of fibers 20. (Collectingfibers on generally flat collector surface 19 should be distinguishedfrom e.g. collecting fibers in a gap between spaced-apart surfaces).Collector surface 19 may comprise a single, continuous collector surfacesuch as provided by a continuous belt or a drum or roll with a radius ofat least six inches. Collector 19 may be generally porous andgas-withdrawal (vacuum) device 14 can be positioned below the collectorto assist deposition of fibers onto the collector (porosity, e.g.,relatively small-scale porosity, of the collector does not change thefact that the collector is generally flat as defined above). Thedistance 21 between the attenuator exit and the collector may be variedto obtain different effects. Also, prior to collection, extrudedfilaments may be subjected to a number of additional processing stepsnot illustrated in FIG. 1, e.g., further drawing, spraying, etc.

After collection, the collected mass 20 (web) of spunbonded fibers maybe subjected to one or more bonding operations, e.g. to enhance theintegrity and/or handleability of the web. In certain embodiments, suchbonding may comprise autogeneous bonding, defined herein as bondingperformed at an elevated temperature (e.g., as achieved by use of anoven and/or a stream of controlled-temperature air) without theapplication of solid contact pressure onto the web. Such bonding may beperformed by the directing of heated air onto the web, e.g. by the useof controlled-heating device 101 of FIG. 1. Such devices are discussedin further detail in U.S. Patent Application 2008/0038976 to Berrigan etal., which is incorporated by reference herein for this purpose. Inaddition to, or in place of, such bonding, other well known bondingmethods such as the use of calendering rolls, may be employed.Spunbonded web 20 may be conveyed to other apparatus such as embossingstations, laminators, cutters and the like, wound into a storage roll,etc.

FIG. 2 is an enlarged side view of an exemplary attenuator 16 throughwhich filaments 15 may pass. Attenuator 16 may serve to at leastpartially draw filaments 15 and may serve to cool and/or quenchfilaments 15 additionally (beyond any cooling and/or quenching offilaments 15 which may have already occurred in passing through thedistance between extrusion head 10 and attenuator 16). Such at leastpartial drawing may serve to achieve at least partial orientation of atleast a portion of each filament, with commensurate improvement instrength of the solidified fibers produced therefrom, as is well knownby those of skill in the art. Such at least partial drawing may also bemanifested in a reduction in the diameter of the solidified fiber fromwhat the diameter would be in the absence of drawing. In general, areduction in the amount of drawing (e.g., a reduction in the volume ofdrawing air used in attenuator 16) performed on fibers is expected bythose of ordinary skill in the art to result in fibers that may beweaker (due to their lack of orientation) and/or larger in diameter.

Exemplary attenuator 16 in some cases may comprise two halves or sides16 a and 16 b separated so as to define between them an attenuationchamber 24, as in the design of FIG. 2. Although existing as two halvesor sides (in this particular instance), attenuator 16 functions as oneunitary device and will be first discussed in its combined form.Exemplary attenuator 16 includes slanted entry walls 27, which define anentrance space or throat 24 a of the attenuation chamber 24. The entrywalls 27 preferably are curved at the entry edge or surface 27 a tosmooth the entry of air streams carrying the extruded filaments 15. Thewalls 27 are attached to a main body portion 28, and may be providedwith a recessed area 29 to establish an air gap 30 between the bodyportion 28 and wall 27. Air may be introduced into the gaps 30 throughconduits 31. The attenuator body 28 may be curved at 28 a to smooth thepassage of air from the air knife 32 into chamber 24. The angle (α) ofthe surface 28 b of the attenuator body can be selected to determine thedesired angle at which the air knife impacts a stream of filamentspassing through the attenuator.

Attenuation chamber 24 may have a uniform gap width; or, as illustratedin FIG. 2, the gap width may vary along the length of the attenuatorchamber. The walls defining at least a portion of the longitudinallength of the attenuation chamber 24 may take the form of plates 36 thatare separate from, and attached to, the main body portion 28.

In some embodiments, certain portions of attenuator 16 (e.g., sides 16 aand 16 b) may be able to move toward one another and/or away from oneanother, e.g. in response to a perturbation of the system. Such abilitymay be advantageous in some circumstances.

Further details of attenuator 16 and possible variations thereof arefound in U.S. Patent Application 2008/0038976 to Berrigan et al. and inU.S. Pat. Nos. 6,607,624 and 6,916,752, all of which are incorporatedherein by reference for this purpose.

The inventors have found that, in deviating from the conventionaloperation of spunbonding processes (e.g., in deviating from the ordinaryoperation (e.g. as described in the above-referenced sources) of theapparatus of FIGS. 1 and 2), unique and advantageous webs can beproduced, as described herein.

Specifically, the inventors have discovered that upon proper selectionat least of the amount of quenching air and drawing air used, relativeto the amount of molten polymer throughput (e.g., the throughput rate offilaments being meltspun), spunbonded webs with unique properties can beproduced. Briefly, such webs may have an unexpected combination of highloft and a high ratio of Effective Fiber Diameter (EFD) to Actual FiberDiameter (AFD), as discussed later herein in detail. Such a combinationof high loft and a high ratio of EFD to AFD may impart these webs with aunique ability to function as a depth filter; e.g., to be able tocollect a relatively high loading of particles within the filter webprior to particles forming a surface cake on the surface of the filterweb.

The loft of such webs will be characterized herein in terms of solidity(as defined herein and as measured by methods reported herein). Asdisclosed herein, webs of solidity from about 4.0% to less than 8.0%(i.e. of loft of from about 96.0% to greater than 92.0%) can beproduced. In various embodiments, webs as disclosed herein comprise asolidity of at most about 7.5%, at most about 7.0%, or at most about6.5%. In further embodiments, webs as disclosed herein comprise asolidity of at least about 5.0%, at least about 5.5%, or at least about6.0%.

In various embodiments, spunbonded webs as disclosed herein comprise aratio of Effective Fiber Diameter to Actual Fiber Diameter of at leastabout 1.40, at least about 1.50, or at least about 1.60.

Certain high-loft webs as heretofore reported by other workers in thefield have relied on the presence of crimped fibers (as previouslydefined herein) to achieve high loft. Webs as described herein do notneed to contain crimped fibers in order to achieve high loft. Thus, insome embodiments, webs as disclosed herein are substantially free ofcrimped fibers, which in this context means that less than one of everyten fibers of the web is a crimped fiber as defined herein. In furtherembodiments, less than one of every twenty fibers of the web is acrimped fiber as defined herein. (An exemplary web meeting thesecriteria is shown in FIGS. 4 and 5). Those of ordinary skill in the artwill of course readily appreciate the difference between such nonlinear(e.g., curved) fibers or portions thereof, as may occur in the course offorming any spunbonded web, and crimped fibers as defined herein. Inparticular embodiments, webs as described herein are substantially freeof crimped staple fibers.

Often, high-loft webs in the art rely on the use of so-calledbicomponent fibers which, upon particular thermal exposures (e.g.,thermal activation), may undergo crimping (e.g., by virtue of the twocomponents of the fiber being present in a side-by-side or eccentricsheath-core configuration and having different shrinkagecharacteristics, as is well known in the art). Although bicomponentfibers may be optionally present in webs as disclosed herein, the websas disclosed herein do not need to contain bicomponent fibers in orderto achieve high loft. Thus, in some embodiments, webs as disclosedherein are substantially free of bicomponent fibers, which as definedherein means that less than one of every ten fibers of the web is madefrom a bicomponent resin (i.e. with the balance of the fibers comprisingmonocomponent fibers). In further embodiments, less than one of everytwenty fibers of the web is a bicomponent fiber as defined herein. Inspecific embodiments, webs as disclosed herein comprise monocomponentspunbonded webs, which is defined herein as meaning that the webgenerally contains only monocomponent fibers (i.e. with bicomponentfibers being present at less than one fiber per fifty fibers of theweb). Such monocomponent webs of course do not preclude the presence ofadditives, processing aids, and the like, which may be present in theweb (whether as e.g. particulate additives interspersed in the web or ase.g. melt additives present within the material of individual fibers).

In minimizing the amount of bicomponent fibers present, webs asdisclosed herein may be advantageous in at least certain embodiments.For example, webs as disclosed herein may be comprised of monocomponentfibers that are comprised substantially of polypropylene, which may bevery amenable to being charged (e.g., if desired for filtrationapplications). Bicomponent fibers which comprise an appreciable amountof e.g. polyethylene may not be as able to be charged due to the lesserability of polyethylene to accept and retain an electrical charge. Webscomprised primarily of monocomponent fibers as disclosed herein may haveadditional advantages over bicomponent fibers in that high loft may beachieved without the necessity of a thermal activation step.

Certain high-loft webs as heretofore reported by other workers in thefield have relied on the presence of gap-formed fibers as definedherein. Webs of this type may comprise a significant number of fiberportions which are oriented in the z-direction (thickness direction) ofthe web. Such fibers may, when the web is viewed in cross section,exhibit e.g. loops, waves, ridges, peaks, folds, U-shapes or C-shapes(with the closed end of the U or C being generally positioned closer toan interior portion of the web and the arms of the U or C beingpositioned further from an interior portion of the web). The z-axisterminii of such fibers may be fused into the surfaces of the web.

Webs as disclosed herein do not need to contain gap-formed fibers inorder to achieve high loft. Thus, in some embodiments, webs as disclosedherein are substantially free of gap-formed fibers, which as definedherein means that less than one of every twenty fibers of the web is agap-formed fiber. An exemplary web meeting this criteria is shown inFIGS. 4 and 5. (Those of ordinary skill in the art will readilyappreciate that in the formation of any spunbonded web, some smallnumber of fibers may form structures resembling those exhibited bygap-formed fibers. Those of ordinary skill in the art will furtherappreciate that such occurrences can easily be distinguished from a webmade of gap-formed fibers). In particular embodiments, webs as disclosedherein are substantially free of repeating patterns of C-shaped fibers,U-shaped fibers, and the like, and are substantially free of repeatingpatterns folds, loops, ridges, peaks, and the like. In furtherembodiments, webs as disclosed herein do not comprise a plurality offibers in which the z-axis terminii of the fibers are fused into thesurfaces of the web.

In producing high loft webs via the use of a single, relativelyconventional, generally flat collecting surface (e.g., as shown in FIG.1), the processes disclosed herein advantageously avoid the complexarrangements of spaced-apart collecting surfaces that are typicallyrequired in order to provide gap-formed fibers.

Webs as disclosed herein have been found by the inventors to exhibitunique characteristics which have not been reported heretofore.Specifically, the inventors have characterized these webs by comparingthe Actual Fiber Diameter (AFD) of the fibers of the web, to theEffective Fiber Diameter (EFD) exhibited by the web. As explained indetail in the Examples section, the Actual Fiber Diameter is obtained bymicroscopic observation and represents the (average) actual physicaldiameter of the fibers. The Effective Fiber Diameter is a calculatedparameter (computed from the measured pressure drop and flowrate throughthe web) obtained from a well-known model (Davies, C. N.; The Separationof Airborne Dust and Particles, Institution of Mechanical Engineers,London, Proceedings 1B, 1952) based on fundamental principles of fluidflow through a porous media. In essence, the Effective Fiber Diameter ofa web represents the fiber diameter that would be expected to give riseto the flow properties exhibited by the web, according to the fluid flowmodel. Those of ordinary skill in the art appreciate that (while thecorrespondence may not be exact) for a given spunbonded web, theEffective Fiber Diameter is often very similar to (e.g., within about20% of) the Actual Fiber Diameter.

The inventors have found that high-loft webs as disclosed hereinunexpectedly exhibit an Effective Fiber Diameter which is at least about40% greater than the Actual Fiber Diameter of the web, as seen in Table5 of the Examples section. For example, web 4A of Example 4 displays anEffective Fiber Diameter (19.2 μm) that is around 50% greater than theActual Fiber Diameter (12.6 μm) of the web (That is, the EFD/AFD ratiois approximately 1.52). In contrast, the web of Comparative Example 1displays an Effective Fiber Diameter (14.0 μm) that is less than 10%greater than the Actual Fiber Diameter (13.0 μm) of the web ofComparative Example 1.

Those of ordinary skill in the art will appreciate that the increase inthe EFD/AFD ratio of web 4A, versus that of the web of ComparativeExample 1, occurs despite the fact that both webs display quite similarActual Fiber Diameters (12.6 μm versus 13.0 μm). Further, the 4A web andthe Comparative Example 1 web were both made on the same apparatus (withthe Comparative Example 1 web made using ordinary operating conditionssimilar to those described in the art, and with the 4A web being madeaccording to the methods disclosed herein). Thus, altering the operatingconditions by the methods disclosed herein did not result in asignificant change in the actual diameter of the fibers of the web (norin unacceptable lowering of the strength of the fibers), but did resultin a significantly higher Effective Fiber Diameter, as well as asignificantly higher loft.

Those of ordinary skill in the art will thus appreciate that the methodsdisclosed herein allow meltspun fibers to be produced under conditionsthat allow the fibers to be adequately drawn (as evidenced by the factthat the fibers may be made with similar diameter as made under ordinaryconditions, as discussed above, and also by the fact that the fibershave acceptable strength), while allowing the fibers to unexpectedlyform webs with advantageously high loft and high EFD/AFD ratios.

While not wishing to be limited by theory or mechanism, the inventorspostulate that, since such significantly higher Effective FiberDiameters may be seen even in cases in which the Actual Fiber Diametersare quite similar, such differences in Effective Fiber Diameter may bedue to the fibers being collectively arranged in some novelconfiguration achieved by the procedures disclosed herein.

The inventors have found that such novel and useful webs as disclosedherein can be produced by significantly reducing the amount of quenchingair and/or drawing air used, relative to the throughput rate of moltenpolymer filaments. Such an approach goes against conventional wisdom,which postulates that meltspun fibers should be as completely quenchedas possible before being collected (although some researchers havereported the production of spunbonded fibers without the use ofquenching air as such, such researchers typically still use relativelyhigh amounts of drawing air, which in such case would also perform aquenching function). Such maximally-complete quenching has been thoughtof as being useful to prevent fibers from sticking to the internalsurfaces of an attenuator, from clumping together to form ropyaggregated bundles which can disadvantageously reduce the uniformity ofthe web, and so on.

Unexpectedly, the inventors have found that such reduction of thequenching and/or drawing air relative to the throughput rate of meltspunfibers, in the manner disclosed herein, can provide a web with anunexpectedly high loft and with an unexpectedly high ratio of EFD toAFD, without the necessity of the web containing crimped fibers,gap-formed fibers, bicomponent fibers, and so on, while avoiding theabove-listed expected problems and while providing sufficient drawingfor the fibers to have acceptable strength.

Without wishing to be limited by theory or mechanism, the inventorspostulate that the phenomena disclosed herein may result at least inpart from fibers colliding and bonding together along a segment of theirlength at some point during the spunbonding process. That is, arelatively high number of ropy aggregated bundles (often called“macrobundles”) comprising several (e.g., four, five, or as many aseight or more) fibers which are bonded together along a segment of theirlength (such fibers are occasionally called “married” fibers) may beadvantageously formed in the processes disclosed herein. It has been abasic principle among those of ordinary skill in the art that featuressuch as macrobundles are to be avoided or minimized in making spunbondedwebs, as they may stick to the interior of an attenuator and disrupt thespunbonding process, may lead to ropy agglomerates in the collected webwhich imparts undesirable nonuniformity to the web, and so on. Whilesuch macrobundles may be present to some extent in any spunbonded web,(e.g., some may be found in the Comparative Example 1 web of FIG. 3) theinventors postulate that an increased amount of macrobundles may be atleast partially responsible for the unique properties of theherein-disclosed webs.

Macrobundles found in webs as disclosed herein are pointed out(designated by reference number 50) in FIG. 4. In particular, theexemplary web of FIG. 5 illustrates the unique structure of the websdisclosed herein, in which large numbers of macrobundles are present(and may often be oriented generally in the plane of the web). Thisstructure may be contrasted with at least some webs of the art (e.g.,some webs containing gap-formed fibers). Such webs of the art, althoughpossibly comprising high loft as a whole, may comprise a nonuniformstructure in which the interior of the web comprises a relatively highloft and one or both surfaces of the web comprise a relatively low loft(i.e. are more densified). Webs as described herein, in not comprisingrelatively densified surface regions, may be more able to allowparticles to penetrate into, and be retained in, the interior regions ofthe web, which may contribute to the superior depth loading capabilitiesnoted by the inventors.

While once again not wishing to be limited by theory or mechanism, itmay be that the unique design of an attenuator of the type shown in FIG.2, which those of skill in the art will recognize as having a relativelyshort length drawing chamber, may be particularly advantageous inallowing such macrobundles to be successfully generated and incorporatedinto a spunbonded web when operated as described herein.

Webs as disclosed herein thus may be produced by significantly reducingthe amount of drawing air, and optionally the quench air, relative tothe molten polymer throughput. The amounts of drawing air as disclosedherein would be recognized by those of skill in the art as being in therange commonly thought of as being so low as to result in theaforementioned difficulties in operating the meltspinning process,and/or to result in the aforementioned undesirable web features. Thus,the conditions disclosed herein do not fall within the realm of routineoptimization of the ordinary conditions of meltspinning processes.

Examples of webs produced with reduced quench air flow and draw air flow(compared to ordinarily used rates of air flow, relative to the amountof molten polymer throughput) are discussed in Examples 1-3.

The inventors have also found it possible to achieve the resultsdisclosed herein while still using a relatively high amount of quenchingair and/or drawing air, if the molten polymer throughput is increasedsufficiently. An example of a web produced in such a manner is presentedin Example 4. In this case the quench air and draw air were comparableto that of Comparative Example 1, but the molten polymer throughput wasincreased by a factor sufficient to achieve the advantageous resultsdisclosed herein.

Thus, webs as disclosed herein can be produced by significantly reducingthe amount of drawing air, and optionally the quenching air, relative tothe molten polymer throughput, whether this is done e.g. by decreasingthe quenching air and drawing air, or e.g. by increasing the moltenpolymer throughput rate, or some combination of both. While presentedherein are certain combinations of processing conditions that have beenfound to be particularly suitable in use of apparatus of the typepresented herein, those of ordinary skill in the art will appreciatethat the conditions disclosed herein may be somewhat specific to thedesign of the apparatus used herein. A suitable combination of processconditions may have to be obtained for any particular process line,guided by the disclosures herein. And, as mentioned, certain apparatus(e.g., those of the type comprising the innovative attenuator designdiscussed herein) may be most suitable for production of spunbonded websas disclosed herein.

In producing high loft webs as disclosed herein, the method ofcollection of the fibers may also be manipulated to advantage. Forinstance, the amount of vacuum applied to the fiber collection surface(e.g., by gas-withdrawal device 14 shown in FIG. 1) may be held to aminimum, in order to preserve the highest loft (however, and againunexpectedly, webs as disclosed herein have proven to be capable ofretaining high loft even with the use of a relatively large amount ofvacuum). The velocity of collection surface 19 (the forming speed) mayalso be manipulated to advantage, e.g. to further lower the solidity andincrease the loft, as evidenced by Tables 1A and 2A. Likewise, anysubsequent bonding method (which are often used to enhance the integrityand physical strength of a web) may be manipulated to advantage. Thus,in the use of a controlled-heating device 101 of FIG. 1, the flowrate ofany heated air supplied by device 101, and/or the amount of any vacuumapplied in such process (e.g., by way of gas-withdrawal device 14) maybe minimized. Or, in bonding by calendering, the amount of force, and/orthe actual area of calendering, may be held to a minimum (e.g.,point-bonding may be used). With particular regard to calendering, ifsuch calendering is performed so that it significantly densifies the webareas that receive calendering force, and such that a relatively largearea of the web is so calendered, the densified areas may alter certainmeasured properties of the web (e.g., the Effective Fiber Diameter) fromthat inherently achieved by the web prior to being calendered (and fromthat exhibited by the areas of the web that did not receive calenderingforce). Thus, in the particular case of webs which have been socalendered, it may be necessary to test uncalendered areas of a web,and/or to test the web in its precalendered condition, to determinewhether the web falls within the parameters disclosed herein.

As mentioned, webs as disclosed herein may comprise fibers that havebeen exposed to a relatively low rate or degree of quenching, and/or toa relatively low rate or degree of drawing, in accordance with thedisclosures herein. As such, in various embodiments webs as disclosedherein may comprise fibers that do not include longitudinal segmentsthat differ in birefringence by 5% or more; and/or, fibers in which in aGraded Density test (as disclosed in U.S. Pat. No. 6,916,752 to Berriganet al.) less than five fiber pieces become disposed at an angle at least60 degrees from horizontal.

In some embodiments, webs as disclosed herein may comprise “directlycollected fibers” as defined herein.

In some embodiments, webs as disclosed herein may comprise generallycontinuous fibers, meaning fibers of relatively long (e.g., greater thansix inches), indefinite length. Such generally continuous fibers may becontrasted with e.g. staple fibers which are often relatively short(e.g., six inches or less) and/or chopped to a definite length.

In various embodiments, basis weights of webs as disclosed herein mayrange e.g. from 30-200 grams per square meter. In various embodiments,webs as disclosed herein may range from about 0.5 mm in thickness toabout 3.0 mm in thickness.

In some embodiments, webs as disclosed herein are self-supporting,meaning that they comprise sufficient integrity to be handleable usingnormal processes and equipment (e.g., can be wound up into a roll,pleated, assembled into a filtration device, etc.). As mentioned herein,bonding processes (e.g., autogeneous bonding via a controlled-heatingapparatus, point-bonding, etc.) may be used to enhance thisself-supporting property.

In various embodiments, webs as disclosed herein comprise an ActualFiber Diameter of at least about 10 μm, at least about 14 μm, or atleast about 18 μm. In further embodiments, webs as disclosed hereincomprise an Actual Fiber Diameter of at most about 30 μm, at most about25 μm, or at most about 20 μm.

In various embodiments, webs as disclosed herein comprise an EffectiveFiber Diameter of at least about 15 μm, at least about 20 μm, or atleast about 25 μm. In further embodiments, webs as disclosed hereincomprise an Effective Fiber Diameter of at most about 45 μm, at mostabout 35 μm, or at most about 30 μm.

In various embodiments, any convenient thermoplastic fiber-formingpolymeric material may be used to form webs as disclosed herein. Suchmaterials might include e.g. polyolefins (e.g., polypropylene,polyethylene, etc.), poly(ethylene terephthalate), nylon, and copolymersand/or blends of any of these.

In some embodiments, other fibers, additives, etc. may be added to thewebs disclosed herein. For example, staple fibers may be included,particulate additives for various purposes, sorbents, and the like, maybe used, as is known in the art. In particular, fluorinated additives ortreatments may be present, e.g. if desired in order to improve the oilresistance of the web.

In some embodiments webs as disclosed herein may be charged as is wellknown in the art, for example by hydrocharging, corona charging, and soon.

Additional layers, for example supporting layers, pre-filter layers, andthe like, may be combined (e.g., by lamination) with the webs disclosedherein. Thus, in some embodiments webs disclosed herein may be presentas one or more of sublayers in a multilayer article.

In some embodiments, webs as disclosed herein may be pleated as is wellknown in the art, e.g., to form a pleated filter for use in applicationssuch as air filtration. As mentioned previously, those of ordinary skillin the art will distinguish such pleating of a web as a whole fromcrimping of individual fibers. Pleated filters as described herein maybe self-supporting, meaning that they do not collapse or bow excessivelywhen subjected to the air pressure typically encountered in forced airventilation systems. Pleated filters as described herein may compriseone or more scrims and/or a perimeter frame to enhance the stability ofthe pleated filter. FIG. 6 shows an exemplary pleated filter 114 withcontaining filter media comprised of spunbonded web 20 as describedherein, and further comprising perimeter frame 112 and scrim 110.Although shown in FIG. 6 as a planar construction in discontinuouscontact with one face of the filter media, scrim 110 may be pleatedalong with the filter media (e.g., so as to be in substantiallycontinuous contact with the filter media). Scrim 110 may be comprised ofnonwoven material, wire, fiberglass, and so on.

Possibly due to their high loft and high ratio of Effective FiberDiameter to Actual Fiber Diameter allowing them to function as depthfilters, webs as described herein can exhibit advantageous filtrationproperties, for example high filtration efficiency in combination withlow pressure drop. Such properties may be characterized by any of thewell known parameters including percent penetration, pressure drop,Quality Factor, capture efficiency (e.g., Minimum Composite Efficiency,Minimum Efficiency Reporting Value), and the like. In particularembodiments, webs as disclosed herein comprise a Quality Factor of atleast about 0.5, at least about 0.7, or at least about 1.0.

EXAMPLES Test Procedures

Solidity and Loft

Solidity is determined by dividing the measured bulk density of afibrous web by the density of the materials making up the solid portionof the web. Bulk density of a web can be determined by first measuringthe weight (e.g. of a 10-cm-by-10-cm section) of a web. Dividing themeasured weight of the web by the web area provides the basis weight ofthe web, which is reported in g/m². Thickness of the web can be measuredby obtaining (e.g., by die cutting) a 135 mm diameter disk of the weband measuring the web thickness with a 230 g weight of 100 mm diametercentered atop the web. The bulk density of the web is determined bydividing the basis weight of the web by the thickness of the web and isreported as g/m³.

The solidity is then determined by dividing the bulk density of the webby the density of the material (e.g. polymer) comprising the solidfibers of the web. (The density of a polymer can be measured by standardmeans if the supplier does not specify material density.) Solidity is adimensionless fraction which is usually reported in percentage.

Loft is usually reported as 100% minus the solidity (e.g., a solidity of7% equates to a loft of 93%).

Effective Fiber Diameter

The Effective Fiber Diameter (EFD) of a web is evaluated according tothe method set forth in Davies, C. N., ‘The Separation of Airborne Dustand Particles,’ Institution of Mechanical Engineers, London, Proceedings1B, 1952. Unless otherwise noted, the test is run at a face velocity of14 cm/sec.

Actual Fiber Diameter and Web Characterization

The Actual Fiber Diameter (AFD) of fibers in a web is evaluated byimaging the web via a scanning electron microscope at 500 times orgreater magnification and utilizing an Olympus DP2-BSW image analysisprogram. At least 100 individual diameter measurements are obtained foreach web sample and the mean of these measurements is reported as theAFD for that web.

Visual inspection via microscopy (e.g., optical or SEM) may be used indetermining whether a web comprises fibers of a given type (e.g.,crimped fibers, gap-collected fibers, and/or bicomponent fibers). Thiscan be performed by inspection of fiber sections (e.g., appearing in thefield of view of a microscope), without regard as to whether the fibersections may be from individual, separate fibers, or whether at leastsome of the sections inspected may be from fibers that are sufficientlylong so as to loop back within the field of view multiple times. Thus,such characterizations as less than one of every twenty fibers being ofa given type, are defined herein as meaning that less than one of everytwenty fiber sections, as evaluated in the course of a visual inspection(of an appropriate number of different areas of the web), is of thegiven type.

% Penetration, Pressure Drop, and Quality Factor

Percent penetration, pressure drop and the filtration Quality Factor(QF) of a web sample is determined using a challenge aerosol containingDOP (dioctyl phthalate) liquid droplets, delivered (unless otherwiseindicated) at a flow rate of 85 liters/min to provide a face velocity of14 cm/s, and evaluated using a TSI™ Model 8130 high-speed automatedfilter tester (commercially available from TSI Inc.). For DOP testing,the aerosol may contain particles with a diameter of about 0.185 μm, andthe Automated Filter Tester may be operated with the heater off and theparticle neutralizer on. Calibrated photometers may be employed at thefilter inlet and outlet to measure the particle concentration and the %particle penetration through the filter. An MKS pressure transducer(commercially available from MKS Instruments) may be employed to measurepressure drop (ΔP, mm H₂O) through the filter. The equation:

${QF} = \frac{- {\ln\left( \frac{\%\mspace{14mu}{Particle}\mspace{14mu}{Penetration}}{100} \right)}}{\Delta\; P}$may be used to calculate QF. The initial Quality Factor QF value usuallyprovides a reliable indicator of overall performance, with higherinitial QF values indicating better filtration performance and lowerinitial QF values indicating reduced filtration performance. Units of QFare inverse pressure drop (reported in 1/mm H₂O).

Capture Efficiency

Filtration properties of a filter may be determined by testing insimilar manner to that described in ASHRAE Standard 52.2 (“Method ofTesting General Ventilation Air-Cleaning Devices for Removal Efficiencyby Particle Size”). The test involves configuring the web as a filter(e.g., a pleated and/or framed filter) installing the filter into a testduct and subjecting the filter to potassium chloride particles whichhave been dried and charge-neutralized. A test face velocity of 1.5meters/sec may be employed. An optical particle counter may be used tomeasure the concentration of particles upstream and downstream from thetest filter over a series of twelve particle size ranges or channels.The equation:

${{Capture}\mspace{14mu}{efficiency}\mspace{14mu}(\%)} = {\frac{\begin{matrix}{{{upstream}\mspace{14mu}{particle}\mspace{14mu}{count}} -} \\{{downstream}\mspace{14mu}{particle}\mspace{14mu}{count}}\end{matrix}}{{upstream}\mspace{14mu}{particle}\mspace{14mu}{count}} \times 100}$may be used to determine capture efficiency for each channel. After theinitial efficiency measurement, a sequential series of dust loadings andefficiency measurements are made until the filter pressure reaches apredetermined value; the minimum efficiency for each of the particlesize channels during the test is determined, and the composite minimumefficiency curve is determined. Pressure drop across the filter ismeasured initially and after each dust loading, and both the amount ofdust fed and the weight gain of the filter are determined. From thecomposite minimum efficiency curve, the four efficiency values between0.3 and 1.0 μm may be averaged to provide the E1 Minimum CompositeEfficiency (MCE), the four efficiency values between 1.0 and 3.0 μm maybe averaged to provide the E2 MCE, and the four efficiency valuesbetween 3.0 and 10.0 μm may be averaged to provide the E3 MCE. From theMCE values for a filter, a reference table in the standard may be usedto determine the Minimum Efficiency Reporting Value (MERV) for thefilter.

Example 1

Using an apparatus similar to that shown in FIGS. 1 and 2, monocomponentmonolayer webs were formed from polypropylene having a melt flow rateindex of 70 available from Total Petrochemicals under the tradedesignation 3860. The extrusion head had 18 rows of 36 orifices each,split into two blocks of 9 rows separated by a 0.63 in. (16 mm) gap inthe middle of the die, making a total of 648 orifices. The orifices werearranged in a staggered pattern with 0.25 inch (6.4 mm) spacing. Theflowrate of molten polymer was approximately 0.71 grams per orifice perminute. Two opposed quenching air streams (similar to those shown as 18b in FIG. 1; stream of the type shown as 18 a were not employed) weresupplied as an upper stream from quench boxes 16 in. (406 mm) in heightat an approximate face velocity of 0.3 m/sec and a temperature of 5° C.,and as a lower stream from quench boxes 7.75 in. (197 mm) in height atan approximate face velocity of 0.1 m/sec and ambient room temperature.A movable-wall attenuator similar to that shown in U.S. Pat. Nos.6,607,624 and 6,916,752 was employed, using an air knife gap of 0.030in. (0.76 mm), air fed to the air knife at a pressure of 14 kPa, anattenuator top gap width of 6.1 mm, an attenuator bottom gap width of6.1 mm, and an attenuation chamber length of 6 in. (152 mm). Thedistance from the extrusion head to the attenuator was 31 in. (79 cm),and the distance from the attenuator to the collection belt was 27 in.(69 cm). The meltspun fiber stream was deposited on the collection beltat a width of about 46 cm with a vacuum established under the collectionbelt of approximately 125 Pa. The collection belt was made from 20-meshstainless steel and moved at a velocity (“forming speed”) shown in Table1.

The mass of collected meltspun fibers (web) was then passed underneath acontrolled-heating bonding device to autogeneously bond at least some ofthe fibers together. Air was supplied through the bonding device at avelocity of approximately 4.1 m/sec at the outlet slot, which was 7.6 cmby 61 cm. The air outlet was about 2.5 cm from the collected web as theweb passed underneath the bonding device. The temperature of the airpassing through the slot of the controlled heating device wasapproximately 153° C. as measured at the entry point for the heated airinto the housing. Ambient temperature air was forcibly drawn through theweb after the web passed underneath the bonding device, to cool the webto approximately ambient temperature.

The web thus produced was bonded with sufficient integrity to beself-supporting and handleable using normal processes and equipment; theweb could be wound by normal windup into a storage roll or could besubjected to various operations such as pleating and assembly into afiltration device such as a pleated filter panel.

Several variations of the web were produced, as described in Table 1A.Webs were collected at three different area (basis) weights as achievedby varying the speed of the collection belt. The fibers of one of thewebs (1B) were measured with scanning electron microscopy and found tohave an Actual Fiber Diameter of 17.1 microns with a standard deviationof 2.8 microns based on a sample size of 114 fibers.

Each of the webs (except web 1A, as noted below) was fed through anoff-line (that is, separate from the above-described web-formingprocess) calendering process employing an unheated calendering roll witha 2.4% bonding pattern (the bonding pattern consisted of 3.8 mm tallelements spaced 7.4 mm from row to row and spaced 4.3 mm along eachrow), in combination with a smooth backing roll that was heated to 93°C. and that contacted the patterned roll with a pressure of 18 N/mm anda speed of 15 m/min. The webs were then corona charged at approximately−20 kV using methods well known in the art. Pressure drop at 14 cm/s,Effective Fiber Diameter, % Penetration of DOP, and Quality Factor werethen obtained for these webs, and are listed in Table 1A.

TABLE 1A Property Units 1A 1B 1C 1D Calendered No Yes Yes Yes Formingspeed m/sec 0.56 0.56 0.37 1.12 Basis weight g/m² 73 72 109 38 Thicknessmm 1.5 1.5 2.0 1.0 Pressure drop at 14 cm/s mm H₂O 0.26 0.30 0.55 0.11Solidity % 5.4 5.3 6.1 4.0 Effective fiber diameter μm 35 32 30 36 (EFD)% Penetration DOP at 14 cm/s % 81 80 74 92 Quality factor 1/mm 0.82 0.760.54 0.73 H₂O

Charged flat web samples were laminated to open wire mesh reinforcementwith Super 77 Spray Adhesive available from 3M Company. The laminatedmedia was pleated with a push-bar pleater which was setup to provide 12pleats per foot spacing and a pleat length of approximately 5 cm. Thepleated media was framed into filters with a one-piece die cut frame toprovide a final filter dimension of approximately 35×63×2 cm. Thefilters were evaluated according to ASHRAE Standard 52.2 to a finalpressure of 149 Pa, by an independent testing firm. Minimum CompositeEfficiency and Minimum Efficiency Report Value were obtained for eachpleated filter and are listed Table 1B.

TABLE 1B Property Units 1A 1B 1C 1D Pressure drop (initial) Pa 39 38 5523 E1 MCE (0.3-1.0 μm) % 10 12 22 5 E2 MCE (1-3 μm) % 38 42 55 22 E3 MCE(3-10 μm) % 57 55 69 32 MERV 7 7 7 5 Dust fed g 40.3 29.4 22 59.8 Dustheld g 35.9 25.9 19.7 45.3

Example 2

Using the general method of Example 1 except as otherwise indicatedbelow, monocomponent monolayer webs were formed from 3860 polypropylenehaving a melt flow rate index of 70 available from Total Petrochemicalsand combined with 0.5% by weight Uvinul 5050H available from BASF. Theupper quench stream had an approximate face velocity of 0.4 m/sec. Airfed to the air knife was at a pressure of 34 kPa. The meltspun fiberstream was deposited on the collection belt at a width of about 46 cm.The vacuum under collection belt was estimated to be about 300 Pa. Airwas supplied through the controlled-heating bonding device at a velocityof approximately 5.7 m/sec at the outlet slot. The temperature of theair passing through the slot of the controlled heating device was 155°C. as measured at the entry point for the heated air into the housing.

The web thus produced was bonded with sufficient integrity to beself-supporting and handleable using normal processes and equipment; theweb could be wound by normal windup into a storage roll or could besubjected to various operations such as pleating and assembly into afiltration device such as a pleated filter panel. Several variations ofthe web were produced, as described in Table 2A. Webs were collected atthree different area weights as achieved by varying the speed of thecollection belt. The fibers of web 2B were measured with scanningelectron microscopy and found to have an Actual Fiber Diameter of 15.0microns with a standard deviation of 2.6 microns based on a sample sizeof 252 fibers.

Each of the webs (except web 2A) was calendered in similar manner as forwebs 1B—1D. The webs were then hydrocharged with deionized wateraccording to the techniques taught in U. S. Pat. No. 5,496,507, anddried.

TABLE 2A Property Units 2A 2B 2C 2D Calendered No Yes Yes Yes Formingspeed m/sec 0.62 0.62 0.41 1.24 Basis weight g/m² 69 71 105 33 Thicknessmm 1.4 1.3 1.7 0.8 Pressure drop at 14 cm/s mm H₂O 0.39 0.45 0.78 0.17Solidity % 5.4 6.0 6.6 4.7 Effective fiber diameter (EFD) μm 28 27 25 28% Penetration DOP at 14 cm/s 55 57 37 78 Quality factor 1/mm 1.54 1.271.28 1.53 H₂O

Charged flat web samples were laminated to open wire mesh reinforcement,pleated, framed, and the filters tested, in similar manner as for thesamples of Example 1 Minimum Composite Efficiency and Minimum EfficiencyReport Value were obtained for each pleated filter and are listed Table2B.

TABLE 2B Property Units 2A 2B 2C 2D Pressure drop (initial) Pa 41 46 6426 E1 MCE (0.3-1.0 μm) % 30 30 45 17 E2 MCE (1-3 μm) % 67 68 79 47 E3MCE (3-10 μm) % 84 85 93 61 MERV 8 11 11 7 Dust fed g 23.1 18.2 13.833.1 Dust held g 20.7 16.8 12.8 27.1

Example 3

Using the general method of Example 1 except as otherwise indicatedbelow, a monocomponent monolayer web was formed from 3860 polypropylenehaving a melt flow rate index of 70 available from Total Petrochemicals.The upper quench stream had an approximate face velocity of 0.6 m/sec.The meltspun fiber stream was deposited on the collection belt at awidth of about 46 cm. Air was supplied through the controlled-heatingbonding device at a velocity of approximately 4.6 m/sec at the outletslot.

The web thus produced was bonded with sufficient integrity to beself-supporting and handleable using normal processes and equipment; theweb could be wound by normal windup into a storage roll or could besubjected to various operations such as pleating and assembly into afiltration device such as a pleated filter panel. One variation of theweb was produced, as described in Table 3.

TABLE 3 Property Units 3A Calendered Yes Forming speed m/sec 0.66 Basisweight g/m² 52 Thickness mm 0.9 Pressure drop at 14 cm/s mm H₂O 0.29Solidity % 6.1% Effective fiber diameter (EFD) μm 29

The fibers of web 3A were measured with scanning electron microscopy andfound to have an Actual Fiber Diameter of 19.8 microns with a standarddeviation of 2.8 microns based on a sample size of 146 fibers.

Example 4

Using the general method of Example 1 except as otherwise indicatedbelow, a monocomponent monolayer web was formed from 3860 polypropylenehaving a melt flow rate index of 70 available from Total Petrochemicals.The upper quench stream had an approximate face velocity of 0.7 m/sec; alower quench box was not used. The attenuator had an air knife gap of0.020 in. (0.51 mm); air was fed to the air knife at a pressure of 83kPa. The distance from the extrusion head to the attenuator was 23 in.(58 cm), and the distance from the attenuator to the collection belt was21 in. (53 cm). The meltspun fiber stream was deposited on thecollection belt at a width of about 51 cm. In this case the collectionbelt was a 9 SS TC belt available from Albany International. The vacuumunder the collection belt was estimated to be about 800 Pa. Air wassupplied through the controlled heating bonding device at a velocity ofapproximately 11 m/sec at the outlet slot.

The web thus produced was bonded with sufficient integrity to beself-supporting and handleable using normal processes and equipment; theweb could be wound by normal windup into a storage roll or could besubjected to various operations such as pleating and assembly into afiltration device such as a pleated filter panel. One variation of theweb was produced, as described in Table 4.

TABLE 4 Property Units 4A Calendered No Forming speed m/sec 0.61 Basisweight g/m² 66 Thickness mm 1.0 Pressure drop at 14 cm/s mm H₂O 0.90Solidity % 7.1% Effective fiber diameter (EFD) μm 19

The fibers of web 4A were measured with scanning electron microscopy andfound to have an Actual Fiber Diameter of 12.6 microns with a standarddeviation of 2.5 microns based on a sample size of 191 fibers.

Comparative Example 1

A monocomponent web was formed in accordance with the teachings ofBerrigan, et al., in U.S. Pat. No. 6,916,752. Using the general methodof Example 4 (above) except as otherwise indicated below, a web wasformed from 3860 polypropylene having a melt flow rate index of 70available from Total Petrochemicals. The molten polymer flowrate wasapproximately 0.54 grams per orifice per minute (versus the 0.71 gramsper orifice per minute of Example 4). The vacuum under collection beltwas estimated to be about 2000 Pa.

The web thus produced was bonded with sufficient integrity to beself-supporting and handleable using normal processes and equipment; theweb could be wound by normal windup into a storage roll or could besubjected to various operations such as pleating and assembly into afiltration device such as a pleated filter panel. One variation of theweb was produced, as described in Table C1.

TABLE C1 Property Units 5A Calendered No Forming speed m/sec 0.44 Basisweight g/m² 64 Thickness mm 0.9 Pressure drop at 14 cm/s mm H₂O 1.70Solidity % 8.0% Effective fiber diameter (EFD) μm 14.0

The fibers of web C1 were measured with scanning electron microscopy andfound to have an Actual Fiber Diameter of 13.0 microns with a standarddeviation of 2.2 microns based on a sample size of 147 fibers.

SUMMARY OF EXAMPLES

The Actual Fiber Diameter, the Effective Fiber Diameter, EFD/AFD ratio,and solidity, for Comparative Example 1 (C1) and for samples 1B, 2B, 3Aand 4A are listed in Table 5.

TABLE 5 Effective Actual Fiber Fiber Diameter Solidity Example Diameter(AFD) μm (EFD) μm EFD/AFD (%) C1 13.0 14.0 1.08 8.0 1B 17.1 32.0 1.875.3 2B 15.0 27.0 1.80 6.0 3A 19.8 29.0 1.46 6.1 4A 12.6 19.2 1.52 7.1

The tests and test results described above are intended solely to beillustrative, rather than predictive, and variations in the testingprocedure can be expected to yield different results. All quantitativevalues in the Examples section are understood to be approximate in viewof the commonly known tolerances involved in the procedures used. Theforegoing detailed description and examples have been given for clarityof understanding only. No unnecessary limitations are to be understoodtherefrom.

It will be apparent to those skilled in the art that the specificexemplary structures, features, details, configurations, etc., that aredisclosed herein can be modified and/or combined in numerousembodiments. All such variations and combinations are contemplated bythe inventor as being within the bounds of the conceived invention.Thus, the scope of the present invention should not be limited to thespecific illustrative structures described herein, but rather by thestructures described by the language of the claims, and the equivalentsof those structures. To the extent that there is a conflict ordiscrepancy between this specification and the disclosure in anydocument incorporated by reference herein, this specification willcontrol.

1. A spunbonded web comprising a solidity of from less than 8.0% toabout 4.0% and comprising a ratio of Effective Fiber Diameter to ActualFiber Diameter of at least 1.40, wherein the web is comprised ofmeltspun fibers that are substantially free of crimped fibers,gap-formed fibers, and bicomponent fibers and wherein the web comprisesa perimeter frame along edges of the web.
 2. The web of claim 1 whereinthe web comprises a ratio of Effective Fiber Diameter to Actual FiberDiameter of at least about 1.50.
 3. The web of claim 1 wherein the webcomprises a ratio of Effective Fiber Diameter to Actual Fiber Diameterof at least about 1.60.
 4. The web of claim 1 wherein the web comprisesa solidity of from about 5.0% to about 7.5%.
 5. The web of claim 1wherein the web comprises a solidity of from about 5.5% to about 7.0%.6. The web of claim 1 wherein the web is charged.
 7. The web of claim 6wherein the web is corona charged.
 8. The web of claim 6 wherein the webcomprises a Quality Factor of at least about 0.5.
 9. The web of claim 6wherein the web comprises a Quality Factor of at least about 0.7. 10.The web of claim 6 wherein the web comprises a Quality Factor of atleast about 1.0.
 11. The web of claim 1 wherein the web comprises a massof directly collected fibers.
 12. The web of claim 1 wherein the webcomprises a thickness of at least about 0.8 mm.
 13. The web of claim 1wherein the web has been bonded by autogeneous bonding.
 14. The web ofclaim 1 wherein the web has been point-bonded by calendering.
 15. Theweb of claim 1 wherein at least some of the fibers of the web comprisemacrobundles which comprise segments from at least five fibers bondedtogether.
 16. The web of claim 15 wherein the macrobundles are orientedgenerally in the plane of the web.
 17. The web of claim 1 wherein theActual Fiber Diameter of the web is from about 10 microns to about 25microns.
 18. The web of claim 1 wherein the Effective Fiber Diameter ofthe web is from about 15 microns to about 45 microns.
 19. The web ofclaim 1 wherein the Actual Fiber Diameter of the web is from about 10microns to about 25 microns and the Effective Fiber Diameter of the webis from about 15 microns to about 45 microns.
 20. The web of claim 1wherein the web is a monocomponent spunbonded web.
 21. The web of claim20 wherein the fibers of the web are monocomponent polypropylene fibers.22. The web of claim 1 wherein the web comprises a plurality ofoppositely-facing pleats.
 23. The web of claim 22 wherein the webcomprises a front face and a rear face and wherein the filter comprisesa scrim mounted to a face of the web.
 24. The web of claim 23 whereinthe scrim is pleated along with the filter media so as to be insubstantially continuous contact with the face of the web to which thescrim is mounted.
 25. The web of claim 24 wherein the pleated scrim iscomprised of wire.
 26. The web of claim 23 wherein the scrim is a planarand is in discontinuous contact with the face of the web to which thescrim is mounted.
 27. The web of claim 1 wherein the web is aself-supporting web.